In the processing of petroleum hydrocarbons and feedstocks, such as petroleum processing intermediates, and petrochemicals and petrochemical intermediates, e.g., gas, oils, and reformer stocks, chlorinated hydrocarbons, recycled hydrocarbons, and olefin plant fluids, such as deethanizer bottoms, the hydrocarbons are commonly heated to temperatures of 100.degree. F. to 1050.degree. F., frequently from 390.degree. F. to 800.degree. F. Similarly, such petroleum hydrocarbons are frequently employed as heating mediums on the "hot side" of heating and heating exchange systems. In both instances, the petroleum hydrocarbon liquids are subjected to elevated temperatures which produce a separate phase known as fouling deposits, within the petroleum hydrocarbon. In all cases, these deposits are undesirable by-products.
In many processes, the deposits reduce the bore of conduits and vessels to impede process throughput, impair thermal transfer, and clog filter screens, valves and traps. In the case of heat exchange systems, the deposits form an insulating layer upon the available surfaces to impede heat transfer and necessitate frequent shut-downs for cleaning. Moreover, these deposits reduce throughput, which results in a loss of production capacity with a drastic effect in the yield of finished product. Accordingly, these deposits have caused considerable concern to the industry.
While the nature of the foregoing deposits defies precise analysis, they appear to contain either a combination of carbonaceous phases which are coke-like in nature, polymers or condensates formed from the petroleum hydrocarbons or impurities, catalyst fines and clays/silts present therein and/or salt formation which are primarily composed of magnesium, calcium and sodium chloride salts. Catalysts involved in the formation of such condensates has been attributed to metal compounds such as copper or iron which are present as impurities or acids such as sulfonic acids or Lewis acids. For example, such metals may accelerate the hydrocarbon oxidation rate by promoting degenerative chain branching, and the resultant free radicals may initiate oxidation and polymerization reactions which form gums and sediments. It further appears that the relatively inert carbonaceous deposits are entrained by the more adherent condensates or polymers to thereby contribute to the insulating or thermal opacifying effect.
Fouling deposits are equally encountered in the petrochemical field wherein the petrochemical is either being produced or purified. The deposits in this environment are primarily polymeric in nature and do drastically affect the economies of the petrochemical process. The petrochemical processes include processes ranging from those where ethylene or propylene, for example, are obtained to those wherein chlorinated hydrocarbons are purified.
Other somewhat related processes where antifoulants may be used to inhibit deposit formation are the manufacture of various types of steel or carbon black.
Methods for providing antifoulant inhibition for hydrocarbons during their processing at elevated temperatures with polyalkenylsuccinimides is disclosed in Gonzalez, U.S. Pat. No. 3,271,295 and in Forester, U.S. Pat. Nos. 5,171,420; 5,171,421; and 5,342,505. The use of polyalkenylthiophosphonate esters is disclosed in Forester, U.S. Pat. Nos. 4,578,178; 4,775,458; and 4,972,561. In Forester '178, polyalkenylthiophosphonate esters are used to inhibit fouling deposit formation in a petroleum hydrocarbon during processing thereof at temperatures between 600.degree. and 1000.degree. F. These sulfur-containing esters have alkyl substituents with carbon chain lengths typically greater than 40,while the compounds of the present invention have carbon chain lengths of 40 or less.
In Forester '458 and '561, the same polyalkenylthiophosphonate esters are used in a multi-component composition along with corrosion inhibitors, antioxidants and metal deactivators to control the formation of fouling deposits.